Optical lens module

ABSTRACT

A lens unit ( 20 ) includes a lens body ( 24 ) and a thin film ( 22 ) provided thereon. The thin film comprises a plurality of sections ( 220, 222, 224 ) from a center to a periphery. Each section has a different refractive index. The refractive index of the each section of the thin film increases from the center to the periphery of the lens body/thin film. Such a lens unit can be advantageously incorporated into a compact digital camera.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical lens modules, especially to anoptical lens module for use in, for example, a digital camera.

2. Discussion of Related Art

With the popularization of electronic products such as digital cameras,the requirements for the optical lenses employed therein is everincreasing. In order to provide high imaging quality, the development ofthe optical lenses mainly concentrates on the structure andconfiguration of the optical lenses.

As it is known to those with ordinary skill in the art, light travels atdifferent speeds in different mediums. When a light beam obliquelyenters a second medium with a refractive index n₂ from a first mediumwith a refractive index n₁, the direction of propagation of the lightbeam, at a boundary between the first and second mediums, will change.This change in the propagation direction is the so-called refractionphenomenon. Snell's law discloses that the ratio between the sine ofincident angle and that of refractive angle is constant. This law can beexpressed as below:n₁ sinθ₁=n₂ sinθ₂Wherein n₁ and n₂ represent refractive indices of a first medium and asecond medium, respectively. θ₁ represents an incident angle, and θ₂represents a refractive angle.

According to Snell's law, when light transmits from air to glass, forexample, the refractive index and shape of a lens are main factors indetermining the deflection of the light. Accordingly, the development ofthe optical modules mainly concentrates on the refractive index andshape of the lens.

FIG. 6 shows such a focalization principle, using a conventional lens.This principle discloses that light can be focused and a formatted imagecan be formed with a lens having a proper shape and a smooth surface.

A lens module of a typical digital camera generally includes a pluralityof optical lenses. Generally, in order to obtain a satisfactory imagingperformance, the lens module commonly employs at least three opticallenses. Each optical lens is also referred to as a lens unit.

Referring to FIG. 7, a conventional lens/camera assembly includes a lensmodule 10, a sleeve 14, and a light-receiving unit 12. The lens module10 and the light-receiving unit 12 are received in the sleeve 14. Thelight-receiving unit 12 is arranged at the focus of the lens module 10.The light-receiving unit 12 is configured for converting collected lightsignals into electronic signals.

The lens module 10 includes a plurality of lens units 102 receivedtherein. Each lens units 102 has a different refractive index relativeto the others. By such a configuration of the lens units 102, arelatively short focal length of the lens module 10 may be achieved.Therefore, the volume of the lens module 10 is relatively smaller.However, a plurality of lens units has to be employed, which increasescomplexity and costs of the lens module.

Accordingly, a compact lens module with a lower complexity and cost isneeded.

Therefore, a heretofore-unaddressed need exists in the industry toaddress the aforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

In a preferred embodiment, an optical lens module is provided, whichincludes a lens body and a thin film provided thereon. The thin film,from a center to a periphery of the lens body, is composed of aplurality of film sections. Each film section has a different refractiveindex. The refractive index of each film section of the thin filmincreases from the center to the periphery of the lens body.

The lens body has an optical axis and is advantageouslycentro-symmetrical respective to the optical axis associated therewith.Each film section is also, beneficially, centro-symmetrical with respectto the optical axis of the lens body.

A refractive index of a film section that is located at a center of thethin film is, usefully, equal (or nearly so) to that of the lens body.

Comparing with the conventional lens module, the optical lens module ofthe preferred embodiment has the following advantages. Firstly, only onelens body is needed to acquire the different refractive indices providedby the multi-lens prior art system, which leads to cost reduction.Secondly, the refractive index changes from the central film section tothat of the periphery, thus permitting light to change its directionaccordingly. Thirdly, the optical lens module can focus by itself to geta better image, and thus it should provide for an improved imagequality.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the optical lens module can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present optical lens module.Moreover, in the drawings, like reference numerals designatecorresponding parts throughout the several views.

FIG. 1 is a sectional, schematic view of an optical lens module of apreferred embodiment;

FIG. 2 is a cutaway view of the optical lens module of FIG. 1;

FIG. 3 is a top view of the optical lens module of FIG. 1;

FIG. 4 is a schematic view a focalization principle of the optical lensmodule of FIG. 1;

FIG. 5 is a schematic, cross-sectional view of the optical lens moduleof the preferred embodiment, incorporating the lens unit of FIG. 1;

FIG. 6 is a schematic view showing a focalization principle of aconventional lens; and

FIG. 7 is a schematic, cross-sectional view of a conventional lensassembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 to 3, a lens unit 20 according to a preferredembodiment includes a lens body 24 and a thin film 22 provided thereon.The lens body 24 may be formed of glass or plastic. The lens body 24 hasan optical axis, indicated with a reference letter “a” in FIG. 1. Thelens body 24 is beneficially centro-symmetrical (or at least essentiallyso) with respect to the optical axis “a”. The lens body 24 may besubstantially in a form of a shape selected from the group consisting ofellipsoid, aspherical, and spherical. In the illustrated embodiment, thelens body 24 is a double-convex lens body.

The thin film 22 is formed on a surface of the lens body 24, and has aplurality of film sections with different respective refractive indices.In the illustrated embodiment, the thin film 22 has three sections whenviewed from a top side thereof along a direction parallel to the opticalaxis “a”, i.e., an annular circumferential section 220, an annularintermediate section 222, and a circular top central section 224 (i.e.,a section covering a geometrical center of the thin film 22), arrangedin that order. The circumferential section 220 of the thin film 22 isformed on a circumferential portion of the lens body 24. The top centralsection 224 of the thin film 22 is formed on a top central portion ofthe lens body 24. The intermediate section 222 of the thin film 22 isformed on the lens body 24 between the circumferential section 220 andthe top central section 224. Each of the sections 220, 222, and 224 iscentro-symmetrical with respect to the optical axis “a” of the lens body24. The optical axis “a” passes through an essentially central axis ofthe top central section 224 of the thin film 22. It should be noted thatthe number of sections of the thin film 22 is not limited to theillustrated embodiment. However, the minimum number of sections of thethin film 22 is two.

The refractive index of the thin film 22 gradually increases from thetop central section 224 to the circumferential section 220, with thesections 220, 222, and 224 each having a uniform refractive index andall having substantially the same thickness. In addition, the refractiveindex of the top central section 224 is preferably substantially equalto that of the lens body 24. A refractive index of the lens body 24 isuniform. The refractive indices of the film sections 220, 222, and 224may vary from one another on any basis (e.g., composition) that willproduce the desired gradient in the refractive indices therebetween.

In the illustrated embodiment, each section 220, 222, and 224 of thethin film 22 is made of a glass incorporating at least one of Ag andCsO₂. The concentration of Ag and/or CsO₂ in each section 220, 222, and224 of the thin film 22 may be configured so as to obtain apredetermined refractive index. In the illustrated embodiment, theconcentration of Ag and/or CsO₂ in circumferential section 220 is higherthan that in the top central section 224. It is, however, to beunderstood that the compositions of the sections 220, 222, and 224 couldalso be suitably varied by other means (e.g., alter percentage of one ormore component; and/or add or delete one or more components).

The thin film 22 is opportunely generally formed by a direct currentreactive magnetron sputtering method or by a radio frequency reactivemagnetron sputtering method. Advantageously, an argon gas is used as anenvironmental inert gas, and an oxygen gas is used as an oxidation gas.

In order to reduce loss of light due to reflection, an anti-reflectivefilm (not shown) is beneficially formed on the thin film 22.

According to Snell's law, the larger the refractive index is, thesmaller the refractive angle is. In other words, the direction ofrefractive light deviates more from the original incident direction ofthat light. Referring to FIG. 4, the refractive index of thecircumferential section 220 of the thin film 22 is largest, thus therefractive angle associated therewith is smallest. While the refractiveindex of top central section 224 is smallest, thus the refractive angleis largest. At the central point of the top central section 224, lightenters the lens body 24 without deflecting, whereat therefore, therefractive angle is zero. The net effect of the variance in refractiveindices of the film sections 220, 222, and 224 is that the focal lengthis reduced relative to a lens (e.g., 102) not having such a thin film 22thereon.

Referring to FIG. 5, a present lens assembly/digital camera 50 issubstantially equal to that shown in FIG. 7, except that the lens unit20 is the only one lens unit within the lens module 10 a. The digitalcamera 50 further includes a sleeve 14 a and a light-receiving unit 12.As the lens module 10 a needs to hold only one lens unit 20 as opposedto a plurality of lens units (e.g., 102 in FIG. 7), both the lens module10 a and the sleeve 14 a can be smaller than their counterparts in theprior art lens assembly of FIG. 7. As such, comparing with that in FIG.7, the lens assembly/digital camera 50 of the preferred embodiment shownin FIG. 5 has an advantageous compactness and simplicity. Since there isonly one lens unit 20 needed, the cost of the digital camera 50 isreduced noticeably.

It should be emphasized that the above-described preferred embodiment ismerely a possible example of implementation of the principles of theinvention and is merely set forth for a clear understanding of theprinciples of the invention. Many variations and modifications may bemade to the above-described embodiments without departing substantiallyfrom the spirit and principles of the invention. All such modificationsand variations are intended to be included herein within the scope ofthis disclosure and the present invention and be protected by thefollowing claims.

1. A lens unit, comprising: a lens body and a thin film providedthereon, the thin film comprising a plurality of sections refractiveindices of the sections of the thin film gradually increasing from oneof the sections at the center of the lens body to another one of thesections at the periphery of the lens body.
 2. The lens unit as claimedin claim 1, wherein the number of the sections of the thin film is morethan two.
 3. The lens unit as claimed in claim 1, wherein the lens bodyhas an optical axis, the lens body being essentially centro-symmetricalrespective to the optical axis associated therewith.
 4. The lens unit asclaimed in claim 3, wherein each section of the thin film is essentiallycentro-symmetrical with respect to the optical axis of the lens body. 5.The lens unit as claimed in claim 3, wherein said one of the sections atthe center of the lens body has a refractive index substantially equalto that of the lens body.
 6. The lens unit as claimed in claim 1,wherein the shape of the lens body is selected from one of ellipsoid,aspherical, and spherical.
 7. The lens unit as claimed in claim 1,wherein the thin film is comprised of a glass incorporating at least oneof Ag and CsO₂.
 8. The lens unit as claimed in claim 7, wherein thecontent of at least one of Ag and CsO₂ becomes larger from said one ofthe sections at the center of the lens body to said another one of thesections at the periphery of the lens body.
 9. The lens unit as claimedin claim 1, wherein the lens body is comprised of one of glass andplastic.
 10. A digital camera, comprising: a sleeve; a lens unitreceived in the sleeve, the lens unit having a focus, the lens unitcomprising: a lens body and a thin film provided thereon, the thin filmcomprising a plurality of sections refractive indices of the sections ofthe thin film gradually increasing from one of the sections at thecenter of the lens body to another one of the sections at the peripheryof the lens body; and a light-receiving unit received in the sleeve, thelight-receiving unit being configured for converting light collectedfrom the lens unit into electronic signals.
 11. A lens unit, comprising:a lens body having a surface; and a thin film formed on the surface ofthe lens body, the thin film including a plurality of sectionscontinuously arranged along the surface of the lens body, each of theplurality of sections having a uniform refractive index, the refractiveindices of the plurality of sections gradually increasing from one ofthe sections at a center of the surface of the lens body to another ofthe sections at a periphery of the surface of the lens body.
 12. Thelens unit as claimed in claim 11, wherein the lens body has an opticalaxis, and each of the plurality of sections of the thin film isessentially centro-symmetrical with respect to the optical axis of thelens body.
 13. The lens unit as claimed in claim 12, wherein said one ofthe sections at a center of the surface of the lens body is a circularcentral section, and the plurality of sections of the thin film includethe circular central section and an annular circumferential sectionaround the circular central section, the circular central section andthe annular circumferential section both being centered on the opticalaxis of the lens body.
 14. The lens unit as claimed in claim 13, whereina refractive index of the circular central section is substantiallyequal to that of the lens body.
 15. The lens unit as claimed in claim11, wherein a refractive index of the lens body is uniform, and theplurality of sections of the thin film have substantially the samethickness.
 16. The lens unit as claimed in claim 11, wherein the lensbody is a double-convex lens body, and the thin film is formed on thesurface of both sides of the lens body.
 17. The lens unit as claimed inclaim 11, wherein the thin film is comprised of glass incorporating atleast one of Ag and CsO₂, and the content of at least one of Ag and CsO₂becomes larger from said one of the sections at a center of the surfaceof the lens body to said another of the sections at a periphery of thesurface of the lens body.
 18. The lens unit as claimed in claim 1,wherein the thin film surrounds the lens body, and each of the pluralityof sections has a uniform refractive index.
 19. The digital camera asclaimed in claim 10, wherein a refractive index of the lens body isuniform, and the plurality of sections are continuously distributed on acommon surface of the lens body.
 20. The digital camera as claimed inclaim 10, wherein each of the plurality of sections has a uniformrefractive index, and the plurality of sections of the thin film havesubstantially the same thickness.